1. Field of the Invention
The present application relates generally to atomic layer deposition of thin films comprising silicon and germanium.
2. Background
There has been a growing demand for thin oxide films having a variable range of wet etch rates (WER) compared to conventional thermal oxide or CVD oxide films. Additionally, such films desirably have a conformal step-coverage of greater than 95% on a device structure having an aspect ratio of 10:1 or more.
Atomic layer deposition (“ALD”) is considered a promising method for depositing films having these desired features. As one example, methods for SiO2 film deposition by plasma enhanced atomic layer deposition (“PEALD”) at low temperatures were developed recently; however, the WER range is limited. The WER of SiO2 films remains at about 20 times the WER of conventional thermal oxide. This appears to be the limit on the WER of SiO2 films.
Therefore, there has been research into materials other than SiO2 that could achieve a higher WER. In some research, GeO2 films are considered to be a promising candidate to replace SiO2 in many applications in the future. However, GeO2 is relatively unstable, in part because it is easily dissolved by water and other solutions.